In real world on-road transportation, there are many factors that can affect the overall vehicle fuel economy testing, even if the vehicle design and fuel/lubricants used remain the same. Such factors for heavy duty trucks include, for example, drivers with different operating styles (up to 35% variation in fuel economy), driving speeds (increasing speed from 55 to 75 mph can increase fuel consumption by 50%), payloads (reducing payload by 10,000 pounds increases fuel savings by 4.4%), tires (underinflated tire can reduce fuel efficiency by 3-5%), and the like.
In order to improve fuel economy, techniques are needed to measure fuel economy in vehicles under real operating conditions. There are existing industry test procedures (e.g., SAE J1321 and J1376) for measuring relative fuel economy of on-road vehicles (also known as two-truck tests). These procedures are intended to be used under controlled, warmed-up conditions on a test tract or on suitable roads. Many variables are controlled in the tests, including drivers, elapsed time, cargo weights etc. Due to the controlled environment required, it is very difficult to conduct this type of testing in real world applications.
The development of new and improved energy efficiency tests has been an on-going research effort. What is needed is an improved energy efficiency test for measuring fuel efficiency of on-road vehicles, in particular, a test for improving fuel economy testing precision of on-road vehicles.